/*
** $Id: liolib.c $
** Standard I/O (and system) library
** See Copyright Notice in lua.h
*/

#define liolib_c
#define LUA_LIB

#include "lprefix.h"

#include <ctype.h>
#include <errno.h>
#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "lua.h"

#include "lauxlib.h"
#include "lualib.h"

/*
** Change this macro to accept other modes for 'fopen' besides
** the standard ones.
*/
#if !defined(l_checkmode)

/* accepted extensions to 'mode' in 'fopen' */
#if !defined(L_MODEEXT)
#define L_MODEEXT "b"
#endif

/* Check whether 'mode' matches '[rwa]%+?[L_MODEEXT]*' */
static int l_checkmode(const char *mode)
{
    return (*mode != '\0' && luaport_strchr("rwa", *(mode++)) != NULL &&
            (*mode != '+' || ((void)(++mode), 1)) &&                    /* skip if char is '+' */
            (luaport_strspn(mode, L_MODEEXT) == luaport_strlen(mode))); /* check extensions */
}

#endif

/*
** {======================================================
** l_popen spawns a new process connected to the current
** one through the file streams.
** =======================================================
*/

#if !defined(l_popen) /* { */

#if defined(LUA_USE_POSIX) /* { */

#define l_popen(L, c, m)  (luaport_fflush(NULL), popen(c, m))
#define l_pclose(L, file) (pclose(file))

#elif defined(LUA_USE_WINDOWS) /* }{ */

#define l_popen(L, c, m)  (_popen(c, m))
#define l_pclose(L, file) (_pclose(file))

#if !defined(l_checkmodep)
/* Windows accepts "[rw][bt]?" as valid modes */
#define l_checkmodep(m) ((m[0] == 'r' || m[0] == 'w') && \
                         (m[1] == '\0' || ((m[1] == 'b' || m[1] == 't') && m[2] == '\0')))
#endif

#else /* }{ */

/* ISO C definitions */
#define l_popen(L, c, m)                     \
    ((void)c, (void)m,                       \
     luaL_error(L, "'popen' not supported"), \
     (FILE *)0)
#define l_pclose(L, file) ((void)L, (void)file, -1)

#endif /* } */

#endif /* } */

#if !defined(l_checkmodep)
/* By default, Lua accepts only "r" or "w" as valid modes */
#define l_checkmodep(m) ((m[0] == 'r' || m[0] == 'w') && m[1] == '\0')
#endif

/* }====================================================== */

#if !defined(l_getc) /* { */

#if defined(LUA_USE_POSIX)
#define l_getc(f)       getc_unlocked(f)
#define l_lockfile(f)   flockfile(f)
#define l_unlockfile(f) funlockfile(f)
#else
#define l_getc(f)       luaport_getc(f)
#define l_lockfile(f)   ((void)0)
#define l_unlockfile(f) ((void)0)
#endif

#endif /* } */

/*
** {======================================================
** l_fseek: configuration for longer offsets
** =======================================================
*/

#if !defined(l_fseek) /* { */

#if defined(LUA_USE_POSIX) /* { */

#include <sys/types.h>

#define l_fseek(f, o, w) fseeko(f, o, w)
#define l_ftell(f)       ftello(f)
#define l_seeknum        off_t

#elif defined(LUA_USE_WINDOWS) && !defined(_CRTIMP_TYPEINFO) && defined(_MSC_VER) && (_MSC_VER >= 1400) /* }{ */

/* Windows (but not DDK) and Visual C++ 2005 or higher */
#define l_fseek(f, o, w) _fseeki64(f, o, w)
#define l_ftell(f)       _ftelli64(f)
#define l_seeknum        __int64

#else /* }{ */

/* ISO C definitions */
#define l_fseek(f, o, w) luaport_fseek(f, o, w)
#define l_ftell(f)       luaport_ftell(f)
#define l_seeknum        long

#endif /* } */

#endif /* } */

/* }====================================================== */

#define IO_PREFIX  "_IO_"
#define IOPREF_LEN (sizeof(IO_PREFIX) / sizeof(char) - 1)
#define IO_INPUT   (IO_PREFIX "input")
#define IO_OUTPUT  (IO_PREFIX "output")

typedef luaL_Stream LStream;

#define tolstream(L) ((LStream *)luaL_checkudata(L, 1, LUA_FILEHANDLE))

#define isclosed(p)  ((p)->closef == NULL)

static int io_type(lua_State *L)
{
    LStream *p;
    luaL_checkany(L, 1);
    p = (LStream *)luaL_testudata(L, 1, LUA_FILEHANDLE);
    if (p == NULL)
        luaL_pushfail(L); /* not a file */
    else if (isclosed(p))
        lua_pushliteral(L, "closed file");
    else
        lua_pushliteral(L, "file");
    return 1;
}

static int f_tostring(lua_State *L)
{
    LStream *p = tolstream(L);
    if (isclosed(p))
        lua_pushliteral(L, "file (closed)");
    else
        lua_pushfstring(L, "file (%p)", p->f);
    return 1;
}

static FILE *tofile(lua_State *L)
{
    LStream *p = tolstream(L);
    if (l_unlikely(isclosed(p)))
        luaL_error(L, "attempt to use a closed file");
    lua_assert(p->f);
    return p->f;
}

/*
** When creating file handles, always creates a 'closed' file handle
** before opening the actual file; so, if there is a memory error, the
** handle is in a consistent state.
*/
static LStream *newprefile(lua_State *L)
{
    LStream *p = (LStream *)lua_newuserdatauv(L, sizeof(LStream), 0);
    p->closef = NULL; /* mark file handle as 'closed' */
    luaL_setmetatable(L, LUA_FILEHANDLE);
    return p;
}

/*
** Calls the 'close' function from a file handle. The 'volatile' avoids
** a bug in some versions of the Clang compiler (e.g., clang 3.0 for
** 32 bits).
*/
static int aux_close(lua_State *L)
{
    LStream *p = tolstream(L);
    volatile lua_CFunction cf = p->closef;
    p->closef = NULL; /* mark stream as closed */
    return (*cf)(L);  /* close it */
}

static int f_close(lua_State *L)
{
    tofile(L); /* make sure argument is an open stream */
    return aux_close(L);
}

static int io_close(lua_State *L)
{
    if (lua_isnone(L, 1))                              /* no argument? */
        lua_getfield(L, LUA_REGISTRYINDEX, IO_OUTPUT); /* use default output */
    return f_close(L);
}

static int f_gc(lua_State *L)
{
    LStream *p = tolstream(L);
    if (!isclosed(p) && p->f != NULL)
        aux_close(L); /* ignore closed and incompletely open files */
    return 0;
}

/*
** function to close regular files
*/
static int io_fclose(lua_State *L)
{
    LStream *p = tolstream(L);
    int res = luaport_fclose(p->f);
    return luaL_fileresult(L, (res == 0), NULL);
}

static LStream *newfile(lua_State *L)
{
    LStream *p = newprefile(L);
    p->f = NULL;
    p->closef = &io_fclose;
    return p;
}

static void opencheck(lua_State *L, const char *fname, const char *mode)
{
    LStream *p = newfile(L);
    p->f = luaport_fopen(fname, mode);
    if (l_unlikely(p->f == NULL))
        luaL_error(L, "cannot open file '%s' (%s)", fname, luaport_strerror(luaport_errno));
}

static int io_open(lua_State *L)
{
    const char *filename = luaL_checkstring(L, 1);
    const char *mode = luaL_optstring(L, 2, "r");
    LStream *p = newfile(L);
    const char *md = mode; /* to traverse/check mode */
    luaL_argcheck(L, l_checkmode(md), 2, "invalid mode");
    p->f = luaport_fopen(filename, mode);
    return (p->f == NULL) ? luaL_fileresult(L, 0, filename) : 1;
}

/*
** function to close 'popen' files
*/
static int io_pclose(lua_State *L)
{
    LStream *p = tolstream(L);
    luaport_errno = 0;
    return luaL_execresult(L, l_pclose(L, p->f));
}

static int io_popen(lua_State *L)
{
    const char *filename = luaL_checkstring(L, 1);
    const char *mode = luaL_optstring(L, 2, "r");
    LStream *p = newprefile(L);
    luaL_argcheck(L, l_checkmodep(mode), 2, "invalid mode");
    p->f = l_popen(L, filename, mode);
    p->closef = &io_pclose;
    return (p->f == NULL) ? luaL_fileresult(L, 0, filename) : 1;
}

static int io_tmpfile(lua_State *L)
{
    LStream *p = newfile(L);
    p->f = luaport_tmpfile();
    return (p->f == NULL) ? luaL_fileresult(L, 0, NULL) : 1;
}

static FILE *getiofile(lua_State *L, const char *findex)
{
    LStream *p;
    lua_getfield(L, LUA_REGISTRYINDEX, findex);
    p = (LStream *)lua_touserdata(L, -1);
    if (l_unlikely(isclosed(p)))
        luaL_error(L, "default %s file is closed", findex + IOPREF_LEN);
    return p->f;
}

static int g_iofile(lua_State *L, const char *f, const char *mode)
{
    if (!lua_isnoneornil(L, 1)) {
        const char *filename = lua_tostring(L, 1);
        if (filename)
            opencheck(L, filename, mode);
        else {
            tofile(L); /* check that it's a valid file handle */
            lua_pushvalue(L, 1);
        }
        lua_setfield(L, LUA_REGISTRYINDEX, f);
    }
    /* return current value */
    lua_getfield(L, LUA_REGISTRYINDEX, f);
    return 1;
}

static int io_input(lua_State *L)
{
    return g_iofile(L, IO_INPUT, "r");
}

static int io_output(lua_State *L)
{
    return g_iofile(L, IO_OUTPUT, "w");
}

static int io_readline(lua_State *L);

/*
** maximum number of arguments to 'f:lines'/'io.lines' (it + 3 must fit
** in the limit for upvalues of a closure)
*/
#define MAXARGLINE 250

/*
** Auxiliary function to create the iteration function for 'lines'.
** The iteration function is a closure over 'io_readline', with
** the following upvalues:
** 1) The file being read (first value in the stack)
** 2) the number of arguments to read
** 3) a boolean, true iff file has to be closed when finished ('toclose')
** *) a variable number of format arguments (rest of the stack)
*/
static void aux_lines(lua_State *L, int toclose)
{
    int n = lua_gettop(L) - 1; /* number of arguments to read */
    luaL_argcheck(L, n <= MAXARGLINE, MAXARGLINE + 2, "too many arguments");
    lua_pushvalue(L, 1);         /* file */
    lua_pushinteger(L, n);       /* number of arguments to read */
    lua_pushboolean(L, toclose); /* close/not close file when finished */
    lua_rotate(L, 2, 3);         /* move the three values to their positions */
    lua_pushcclosure(L, io_readline, 3 + n);
}

static int f_lines(lua_State *L)
{
    tofile(L); /* check that it's a valid file handle */
    aux_lines(L, 0);
    return 1;
}

/*
** Return an iteration function for 'io.lines'. If file has to be
** closed, also returns the file itself as a second result (to be
** closed as the state at the exit of a generic for).
*/
static int io_lines(lua_State *L)
{
    int toclose;
    if (lua_isnone(L, 1))
        lua_pushnil(L);                               /* at least one argument */
    if (lua_isnil(L, 1)) {                            /* no file name? */
        lua_getfield(L, LUA_REGISTRYINDEX, IO_INPUT); /* get default input */
        lua_replace(L, 1);                            /* put it at index 1 */
        tofile(L);                                    /* check that it's a valid file handle */
        toclose = 0;                                  /* do not close it after iteration */
    } else {                                          /* open a new file */
        const char *filename = luaL_checkstring(L, 1);
        opencheck(L, filename, "r");
        lua_replace(L, 1); /* put file at index 1 */
        toclose = 1;       /* close it after iteration */
    }
    aux_lines(L, toclose); /* push iteration function */
    if (toclose) {
        lua_pushnil(L);      /* state */
        lua_pushnil(L);      /* control */
        lua_pushvalue(L, 1); /* file is the to-be-closed variable (4th result) */
        return 4;
    } else
        return 1;
}

/*
** {======================================================
** READ
** =======================================================
*/

/* maximum length of a numeral */
#if !defined(L_MAXLENNUM)
#define L_MAXLENNUM 200
#endif

/* auxiliary structure used by 'read_number' */
typedef struct {
    FILE *f;                    /* file being read */
    int c;                      /* current character (look ahead) */
    int n;                      /* number of elements in buffer 'buff' */
    char buff[L_MAXLENNUM + 1]; /* +1 for ending '\0' */
} RN;

/*
** Add current char to buffer (if not out of space) and read next one
*/
static int nextc(RN *rn)
{
    if (l_unlikely(rn->n >= L_MAXLENNUM)) { /* buffer overflow? */
        rn->buff[0] = '\0';                 /* invalidate result */
        return 0;                           /* fail */
    } else {
        rn->buff[rn->n++] = rn->c; /* save current char */
        rn->c = l_getc(rn->f);     /* read next one */
        return 1;
    }
}

/*
** Accept current char if it is in 'set' (of size 2)
*/
static int test2(RN *rn, const char *set)
{
    if (rn->c == set[0] || rn->c == set[1])
        return nextc(rn);
    else
        return 0;
}

/*
** Read a sequence of (hex)digits
*/
static int readdigits(RN *rn, int hex)
{
    int count = 0;
    while ((hex ? isxdigit(rn->c) : isdigit(rn->c)) && nextc(rn))
        count++;
    return count;
}

/*
** Read a number: first reads a valid prefix of a numeral into a buffer.
** Then it calls 'lua_stringtonumber' to check whether the format is
** correct and to convert it to a Lua number.
*/
static int read_number(lua_State *L, FILE *f)
{
    RN rn;
    int count = 0;
    int hex = 0;
    char decp[2];
    rn.f = f;
    rn.n = 0;
    decp[0] = lua_getlocaledecpoint(); /* get decimal point from locale */
    decp[1] = '.';                     /* always accept a dot */
    l_lockfile(rn.f);
    do {
        rn.c = l_getc(rn.f);
    } while (isspace(rn.c)); /* skip spaces */
    test2(&rn, "-+");        /* optional sign */
    if (test2(&rn, "00")) {
        if (test2(&rn, "xX"))
            hex = 1; /* numeral is hexadecimal */
        else
            count = 1; /* count initial '0' as a valid digit */
    }
    count += readdigits(&rn, hex);                      /* integral part */
    if (test2(&rn, decp))                               /* decimal point? */
        count += readdigits(&rn, hex);                  /* fractional part */
    if (count > 0 && test2(&rn, (hex ? "pP" : "eE"))) { /* exponent mark? */
        test2(&rn, "-+");                               /* exponent sign */
        readdigits(&rn, 0);                             /* exponent digits */
    }
    luaport_ungetc(rn.c, rn.f); /* unread look-ahead char */
    l_unlockfile(rn.f);
    rn.buff[rn.n] = '\0'; /* finish string */
    if (l_likely(lua_stringtonumber(L, rn.buff)))
        return 1;       /* ok, it is a valid number */
    else {              /* invalid format */
        lua_pushnil(L); /* "result" to be removed */
        return 0;       /* read fails */
    }
}

static int test_eof(lua_State *L, FILE *f)
{
    int c = luaport_getc(f);
    luaport_ungetc(c, f); /* no-op when c == EOF */
    lua_pushliteral(L, "");
    return (c != EOF);
}

static int read_line(lua_State *L, FILE *f, int chop)
{
    luaL_Buffer b;
    int c;
    luaL_buffinit(L, &b);
    do {                                  /* may need to read several chunks to get whole line */
        char *buff = luaL_prepbuffer(&b); /* preallocate buffer space */
        int i = 0;
        l_lockfile(f); /* no memory errors can happen inside the lock */
        while (i < LUAL_BUFFERSIZE && (c = l_getc(f)) != EOF && c != '\n')
            buff[i++] = c; /* read up to end of line or buffer limit */
        l_unlockfile(f);
        luaL_addsize(&b, i);
    } while (c != EOF && c != '\n'); /* repeat until end of line */
    if (!chop && c == '\n')          /* want a newline and have one? */
        luaL_addchar(&b, c);         /* add ending newline to result */
    luaL_pushresult(&b);             /* close buffer */
    /* return ok if read something (either a newline or something else) */
    return (c == '\n' || lua_rawlen(L, -1) > 0);
}

static void read_all(lua_State *L, FILE *f)
{
    size_t nr;
    luaL_Buffer b;
    luaL_buffinit(L, &b);
    do { /* read file in chunks of LUAL_BUFFERSIZE bytes */
        char *p = luaL_prepbuffer(&b);
        nr = luaport_fread(p, sizeof(char), LUAL_BUFFERSIZE, f);
        luaL_addsize(&b, nr);
    } while (nr == LUAL_BUFFERSIZE);
    luaL_pushresult(&b); /* close buffer */
}

static int read_chars(lua_State *L, FILE *f, size_t n)
{
    size_t nr; /* number of chars actually read */
    char *p;
    luaL_Buffer b;
    luaL_buffinit(L, &b);
    p = luaL_prepbuffsize(&b, n);              /* prepare buffer to read whole block */
    nr = luaport_fread(p, sizeof(char), n, f); /* try to read 'n' chars */
    luaL_addsize(&b, nr);
    luaL_pushresult(&b); /* close buffer */
    return (nr > 0);     /* true iff read something */
}

static int g_read(lua_State *L, FILE *f, int first)
{
    int nargs = lua_gettop(L) - 1;
    int n, success;
    luaport_clearerr(f);
    if (nargs == 0) { /* no arguments? */
        success = read_line(L, f, 1);
        n = first + 1; /* to return 1 result */
    } else {
        /* ensure stack space for all results and for auxlib's buffer */
        luaL_checkstack(L, nargs + LUA_MINSTACK, "too many arguments");
        success = 1;
        for (n = first; nargs-- && success; n++) {
            if (lua_type(L, n) == LUA_TNUMBER) {
                size_t l = (size_t)luaL_checkinteger(L, n);
                success = (l == 0) ? test_eof(L, f) : read_chars(L, f, l);
            } else {
                const char *p = luaL_checkstring(L, n);
                if (*p == '*')
                    p++; /* skip optional '*' (for compatibility) */
                switch (*p) {
                    case 'n': /* number */
                        success = read_number(L, f);
                        break;
                    case 'l': /* line */
                        success = read_line(L, f, 1);
                        break;
                    case 'L': /* line with end-of-line */
                        success = read_line(L, f, 0);
                        break;
                    case 'a':           /* file */
                        read_all(L, f); /* read entire file */
                        success = 1;    /* always success */
                        break;
                    default:
                        return luaL_argerror(L, n, "invalid format");
                }
            }
        }
    }
    if (luaport_ferror(f))
        return luaL_fileresult(L, 0, NULL);
    if (!success) {
        lua_pop(L, 1);    /* remove last result */
        luaL_pushfail(L); /* push nil instead */
    }
    return n - first;
}

static int io_read(lua_State *L)
{
    return g_read(L, getiofile(L, IO_INPUT), 1);
}

static int f_read(lua_State *L)
{
    return g_read(L, tofile(L), 2);
}

/*
** Iteration function for 'lines'.
*/
static int io_readline(lua_State *L)
{
    LStream *p = (LStream *)lua_touserdata(L, lua_upvalueindex(1));
    int i;
    int n = (int)lua_tointeger(L, lua_upvalueindex(2));
    if (isclosed(p)) /* file is already closed? */
        return luaL_error(L, "file is already closed");
    lua_settop(L, 1);
    luaL_checkstack(L, n, "too many arguments");
    for (i = 1; i <= n; i++) /* push arguments to 'g_read' */
        lua_pushvalue(L, lua_upvalueindex(3 + i));
    n = g_read(L, p->f, 2);   /* 'n' is number of results */
    lua_assert(n > 0);        /* should return at least a nil */
    if (lua_toboolean(L, -n)) /* read at least one value? */
        return n;             /* return them */
    else {                    /* first result is false: EOF or error */
        if (n > 1) {          /* is there error information? */
            /* 2nd result is error message */
            return luaL_error(L, "%s", lua_tostring(L, -n + 1));
        }
        if (lua_toboolean(L, lua_upvalueindex(3))) { /* generator created file? */
            lua_settop(L, 0);                        /* clear stack */
            lua_pushvalue(L, lua_upvalueindex(1));   /* push file at index 1 */
            aux_close(L);                            /* close it */
        }
        return 0;
    }
}

/* }====================================================== */

static int g_write(lua_State *L, FILE *f, int arg)
{
    int nargs = lua_gettop(L) - arg;
    int status = 1;
    for (; nargs--; arg++) {
        if (lua_type(L, arg) == LUA_TNUMBER) {
            /* optimization: could be done exactly as for strings */
            int len = lua_isinteger(L, arg) ? luaport_fprintf(f, LUA_INTEGER_FMT,
                                                              (LUAI_UACINT)lua_tointeger(L, arg)) :
                                              luaport_fprintf(f, LUA_NUMBER_FMT,
                                                              (LUAI_UACNUMBER)lua_tonumber(L, arg));
            status = status && (len > 0);
        } else {
            size_t l;
            const char *s = luaL_checklstring(L, arg, &l);
            status = status && (luaport_fwrite(s, sizeof(char), l, f) == l);
        }
    }
    if (l_likely(status))
        return 1; /* file handle already on stack top */
    else
        return luaL_fileresult(L, status, NULL);
}

static int io_write(lua_State *L)
{
    return g_write(L, getiofile(L, IO_OUTPUT), 1);
}

static int f_write(lua_State *L)
{
    FILE *f = tofile(L);
    lua_pushvalue(L, 1); /* push file at the stack top (to be returned) */
    return g_write(L, f, 2);
}

static int f_seek(lua_State *L)
{
    static const int mode[] = { SEEK_SET, SEEK_CUR, SEEK_END };
    static const char *const modenames[] = { "set", "cur", "end", NULL };
    FILE *f = tofile(L);
    int op = luaL_checkoption(L, 2, "cur", modenames);
    lua_Integer p3 = luaL_optinteger(L, 3, 0);
    l_seeknum offset = (l_seeknum)p3;
    luaL_argcheck(L, (lua_Integer)offset == p3, 3,
                  "not an integer in proper range");
    op = l_fseek(f, offset, mode[op]);
    if (l_unlikely(op))
        return luaL_fileresult(L, 0, NULL); /* error */
    else {
        lua_pushinteger(L, (lua_Integer)l_ftell(f));
        return 1;
    }
}

static int f_setvbuf(lua_State *L)
{
    static const int mode[] = { _IONBF, _IOFBF, _IOLBF };
    static const char *const modenames[] = { "no", "full", "line", NULL };
    FILE *f = tofile(L);
    int op = luaL_checkoption(L, 2, NULL, modenames);
    lua_Integer sz = luaL_optinteger(L, 3, LUAL_BUFFERSIZE);
    int res = luaport_setvbuf(f, NULL, mode[op], (size_t)sz);
    return luaL_fileresult(L, res == 0, NULL);
}

static int io_flush(lua_State *L)
{
    return luaL_fileresult(L, luaport_fflush(getiofile(L, IO_OUTPUT)) == 0, NULL);
}

static int f_flush(lua_State *L)
{
    return luaL_fileresult(L, luaport_fflush(tofile(L)) == 0, NULL);
}

/*
** functions for 'io' library
*/
static const luaL_Reg iolib[] = {
    { "close", io_close },
    { "flush", io_flush },
    { "input", io_input },
    { "lines", io_lines },
    { "open", io_open },
    { "output", io_output },
    { "popen", io_popen },
    { "read", io_read },
    { "tmpfile", io_tmpfile },
    { "type", io_type },
    { "write", io_write },
    { NULL, NULL }
};

/*
** methods for file handles
*/
static const luaL_Reg meth[] = {
    { "read", f_read },
    { "write", f_write },
    { "lines", f_lines },
    { "flush", f_flush },
    { "seek", f_seek },
    { "close", f_close },
    { "setvbuf", f_setvbuf },
    { NULL, NULL }
};

/*
** metamethods for file handles
*/
static const luaL_Reg metameth[] = {
    { "__index", NULL }, /* place holder */
    { "__gc", f_gc },
    { "__close", f_gc },
    { "__tostring", f_tostring },
    { NULL, NULL }
};

static void createmeta(lua_State *L)
{
    luaL_newmetatable(L, LUA_FILEHANDLE); /* metatable for file handles */
    luaL_setfuncs(L, metameth, 0);        /* add metamethods to new metatable */
    luaL_newlibtable(L, meth);            /* create method table */
    luaL_setfuncs(L, meth, 0);            /* add file methods to method table */
    lua_setfield(L, -2, "__index");       /* metatable.__index = method table */
    lua_pop(L, 1);                        /* pop metatable */
}

/*
** function to (not) close the standard files stdin, stdout, and stderr
*/
static int io_noclose(lua_State *L)
{
    LStream *p = tolstream(L);
    p->closef = &io_noclose; /* keep file opened */
    luaL_pushfail(L);
    lua_pushliteral(L, "cannot close standard file");
    return 2;
}

static void createstdfile(lua_State *L, FILE *f, const char *k,
                          const char *fname)
{
    LStream *p = newprefile(L);
    p->f = f;
    p->closef = &io_noclose;
    if (k != NULL) {
        lua_pushvalue(L, -1);
        lua_setfield(L, LUA_REGISTRYINDEX, k); /* add file to registry */
    }
    lua_setfield(L, -2, fname); /* add file to module */
}

LUAMOD_API int luaopen_io(lua_State *L)
{
    luaL_newlib(L, iolib); /* new module */
    createmeta(L);
    /* create (and set) default files */
    createstdfile(L, luaport_stdin, IO_INPUT, "stdin");
    createstdfile(L, luaport_stdout, IO_OUTPUT, "stdout");
    createstdfile(L, luaport_stderr, NULL, "stderr");
    return 1;
}
